1. Field of the Invention
The present invention relates to a seal construction of a polymer insulator having a core member, an outer cover member including a sheath portion and sheds, which is arranged on an outer surface of the core member, and securing metal fittings arranged on both ends of the core member, and particularly relates to a seal construction between the outer cover member and the securing metal fitting.
2. Description of Related Art
Generally, a polymer insulator having a core member, an outer cover member including a sheath portion and sheds, which is arranged on an outer surface of the core member, and securing metal fittings arranged on both ends of the core member is known. Moreover, various seal constructions between the outer cover member and the securing metal fitting are also known.
FIG. 4 is a schematic view showing one embodiment of a known seal construction of the polymer insulator. In FIG. 4, a polymer insulator 51 comprises an FRP core 52 as the core member, an outer cover member 55 having a sheath portion 53 and sheds 54, which is arranged on an outer surface of the FRP core 52, and securing metal fittings 56 arranged at both ends of the FRP core 52. In FIG. 4, only one side of the polymer insulator is shown. The securing metal fitting 56 comprises a small diameter portion 61 for securing the FRP core 52 and a large diameter portion 62 arranged continuously from the small diameter portion 61 and having an open end portion 63. A tip portion 71 of the sheath portion 53 is arranged between the large diameter portion 62 and the FRP core 52. Between an inner surface 62a of the large diameter portion 62 and an outer surface 71a of the tip portion 71, a silicon sealant of a room temperature vulcanizing (RTV) type 72 is arranged as a sealant.
Moreover, a protruding portion 72a of the silicon sealant of RTV type 72 is protruded from an end of a portion at which the inner surface 62a of the large diameter portion 62 and the outer surface 71a of the tip portion 71 are connected. In addition, in order to improve a seal property between the inner surface 62a of the large diameter portion 62 and the outer surface 71a of the tip portion 71 of the sheath portion 53, two ring portions 73-1 and 73-2 projected from the outer surface 71a of the tip portion 71 of the sheath portion 53 are arranged.
As mentioned above, in the polymer insulator 51, a connection portion between the outer cover member 55 and the securing metal fitting 56 is very important for preventing in intrusion of rain water which causes a deterioration of the FRP core 52. Therefore, it is necessary to seal such a connection portion, and the connection portion requires a high reliability. In the known seal construction mentioned above, the protruded portion 72a of the sealant 72 is exposed at the open end portion 63 i.e. the sealant 72 is exposed to a natural environment.
Recently, a property of the sealant 72 is improved and it is possible to use the sealant 72 for a use of the polymer insulator 51. However, a property of the sealant 72 is not always equal to that of the outer cover member 55. Therefore, In order to further improve reliability, a seal construction, which does not depend on a property of the sealant 72 even when exposed to a severe natural environment, is desired.
In the known seal construction mentioned above in which the sealant 72 has the protruded portion 72a, if a dimension of the protruded portion 72a is made larger so as to improve a water immersion resistivity by keeping a long seal length, an exposed area of the sealant 72 becomes larger. Therefore, deteriorations due to rain water and ultraviolet rays become more severe, and also an anti-erosion property of the sealant becomes worse. On the other hand, if a dimension of the protruded portion 72a is made smaller so as to improve the problems due to the above deteriorations and antierosion property, it is not possible to maintain a seal reliability.
An object of the invention is to eliminate the drawbacks mentioned above and to provide a seal construction of a polymer insulator which can improve a water intrusion resistivity and prevent an erosion.
According to the invention, a seal construction of a polymer insulator has a core member, an outer cover member including a sheath portion and sheds, which is arranged on an outer surface of the core member, and securing metal fittings arranged on both ends of the core member, wherein a tip portion of the sheath portion is arranged between the securing metal fitting and the core member and a sealant is arranged between an inner surface of the securing metal fitting and an outer surface of the tip portion of the sheath portion. The seal construction includes be following:
(1) a small rib radially projects from the sheath portion of the outer cover member;
(2) a side surface of the small rib is connected to the open end portion of the securing metal fitting via the sealant; and
(3) the sealant does not protrude from a portion between the side surface of the small rib and the open end portion of the securing metal fitting.
In the present invention, by realizing the constructions: a small rib projected from the sheath portion of the outer cover member is arranged; a side surface of the small rib is connected to an open end portion of the securing metal fitting via the sealant; and the sealant is not protruded from a portion between the side surface of the small rib and the open end portion of the securing metal fitting, it is possible to suppress an affect for the sealant due to a rain water, an ultraviolet ray and so on. Therefore, it is possible to obtain an excellent connection life of the sealant and improve a water intrusion resistivity. In addition, it is possible to eliminate a generation of erosion at the protruded portion of the sealant and thus prevent an erosion of the outer cover member.